1. Field of the Invention
The present invention relates to a surface plasmon resonance sensor that utilizes a surface plasmon resonance phenomenon, and particularly relates to a small-size surface plasmon resonance sensor. Further, the present invention relates to a biochip that utilizes this surface plasmon resonance sensor.
2. Description of the Background Art
At present, in the fields of biochemistry and medicine, there is an increasing demand to elucidate with high precision a correlation between physiologically active molecules or the like in a living body. Therefore, small-size sensors capable of measuring with high precision a process or the like of a biochemical reaction of physiologically active molecules or the like have been demanded, and research has been conducted thereon. Among methods used by these sensors, a method that uses a light in measurement is superior in sensitivity, and many schemes such as a calorimetric method, a fluorometric method, and a luminescent method have been developed. However, sensors that use these schemes become large in size, and furthermore, it is reported that a quenching phenomenon due to dye fading may occur. In addition, only sluggish improvement can be achieved in sensitivity of measurement by these schemes. Moreover, the sensors mainly used at present are often configured to conduct measurement in a state where measurement samples are dispersed in a solution. With this configuration, these sensors require a certain optical path length or longer, and this makes it difficult to downsize the sensors.
Accordingly, there have recently been proposed sensors that utilize a sensing method of measuring a reaction occurring at a surface of, or a periphery of the surface of, a substrate onto which living body molecules are fixed. In particular, a sensor that uses surface plasmon resonance spectroscopy is superior in sensitivity and can be downsized as well, and hence attracts attention (e.g. see K. Kurihara et al. Anal Chem. 74 (3): 696-701 (2002) and Shumaker-Parry J S et al. Anal Chem. 76 (4): 918-929 (2004)). Here, FIG. 10 is a schematic cross-sectional view that shows a surface plasmon resonance phenomenon. A description will now be made based on FIG. 10.
An incident beam 100 is incident on a dielectric substrate 82 covered with a metal film 84 through a prism 81. Incident beam 100 passes through dielectric substrate 82 to be reflected by metal film 84, so that an emitted beam 101 is generated through prism 81. At this time, when a certain incident angle and a certain reflection angle are set for operations of incident beam 100 and emitted beam 101, surface plasmon resonance is observed at an interface between metal film 84 and dielectric substrate 82. A surface plasmon resonance sensor that has the configuration shown in FIG. 10 is now under development (e.g. see Japanese Patent Laying-Open No. 2003-279476 and Japanese Patent Laying-Open No. 2003-42944).
However, in the currently-used surface plasmon resonance sensor, it is necessary to dispose a chip and an optical system such that a certain incident angle and a certain reflection angle are achieved, in order to allow incident beam 100 to be incident through prism 81 or a transparent substrate made of quartz or the like, and hence drastic downsizing is difficult.